This invention relates to a hollow bottle having good chemical resistance and excellent fused adhesion strength of the bottom, and the production method therefor. More particularly, the invention relates to a multi-layered bottle which is made by using polyamide resin and the fused adhesion strength of the bottom pinch-off portion of which is quite large as compared with the conventional similar ones.
In the prior art, polyethylene and polypropylene are generally used for producing blow molded bottles, however, they are unsatisfactory in view of the chemical resistance. So that, when the bottles are filled with agricultural medicines and industrial chemicals, the bottles are swollen or, after the passage of a certain time, cracks are caused to occur, therefore, such bottles cannot be used widely in view of the safety. In order to improve the chemical resistance, the use of the resin having good resistance to organic chemicals such as nylon has been proposed.
Thus, the production of single layer bottles made of nylon has been undertaken, however, it has been difficult to produce the nylon bottles because the draw-down phenomenon is caused to occur owing to the low molten viscosity of nylon during the molding operation. Further, the fused adhesion strength of the pinch-off portion in the bottom of nylon single layer bottle is very low so that, if the bottle is dropped, the pinch-off portion is easily separated. Due to the above facts, nylon bottles are not used as the containers for agricultural medicines and industrial chemicals, which are generally filled in metallic cans or glass bottles. It has, however, become a social problem that the wastes of metallic cans and glass bottles after the use thereof are difficulty disposed of. Therefore, the proposal of chemically resistant container has long been desired in place of the above bottles.
As the method for obtaining such improved bottles, for example as shown in Japanese Patent Laid-Open Publication No. Sho. 50-75019 (1975), it is proposed that a double-layer bottle is made of an outer layer of polyolefin containing much inorganic substance such as calcium carbonate and an inner layer of nylon. In the double-layer bottle having such layer structure, however, the fused adhesion strength of the bottom pinch-off portion has not been improved yet.
The fused adhesion strength of the bottom pinch-off portion has a close relationship to the strength in drop test. So that, if the fused adhesion strength of the pinch-off portion is lower than a certain lever, the bottom pinch-off portion is liable to split when the bottle is dropped and it cannot be used safely.
Since the polyolefins such as polyethylene and polypropylene are thermally adhesive, the adhesion strength of the pinch-off portion of the bottle which is made by the conventional blow molding method by using the polyolefin, is satisfactory. While, in the case of nylon, oxide film is formed on the surface because the nylon is liable to receive the influence of oxygen in the air, so that, even through the pinch-off portion looks like to be joined together, the fused adhesion strength of the pinch-off portion is not large enough.
Further, when nylon is used as an inner layer material and a multi-layer parison is inserted into a blow mold and the blow molding is performed by closing the mold, the joined portion is pulled apart and a V-shaped groove is formed in the joined pinch-off portion because a compressed fluid is introduced in the parison during the blow molding and the fused adhesion strength of the inner nylon layer in the pinch-off portion is not satisfactory. Therefore, the area of fused adhesion in pinch-off portion becomes narrow and the fused adhesion strength of the bottom pinch-off portion is largely reduced.